YIG oscillators are a favored form of fundamental electromagnetic energy generators at frequencies in the spectrum of about 1 GHz to about 100 GHz. A YIG oscillator is an oscillator comprising an yttrium iron garnet crystal, which when placed in saturating magnetic field oscillates to generate electromagnetic energy at frequencies related to the strength of the magnetic field. More particularly, the output of a YIG oscillator is linearly dependent on the magnetic flux density in an air gap of a magnetic structure where the YIG crystal is positioned. The magnetic flux density, in turn, is inversely proportional to the length of the air gap, provided that the rest of the parameters of the magnetic circuit are constant.
For example, a 10 GHz YIG oscillator having an air gap length of 1 mm will exhibit a 1 kHz frequency deviation for an air gap length displacement of 1 Angstrom (1E-10 m).
A YIG oscillator structure comprises a metal enclosure enclosing and carrying the electric and magnetic circuitry. The enclosure serves as electrical as well as mechanical interface. Consequently, an external mechanical vibration will propagate into the magnetic structure and affect the length of the air gap, and thus the frequency of the oscillator. Hence, YIG oscillators are sensitive to mechanical vibration and the vibration frequency will appear as a frequency modulation of the YIG oscillator frequency. The modulation frequency is equal to the vibration frequency and the frequency deviation is proportional to the vibration level in terms of g's [m/s.sup.2 ] and the Vibration Sensitivity in terms of frequency deviation vs. vibration level [Hz/g]. Usually the vibration sensitivity is constant vs. vibration frequency superimposed by mechanical resonance peaks.
The YIG oscillator is a low phase-noise device tunable over wide frequency ranges. In applications where the YIG oscillator is used as a low phase-noise source in an environment where mechanical vibrations are present, low Vibration Sensitivity performance is crucial at least for a part of the vibration spectrum. Therefore, attempts have been made to reduce the Vibration Sensitivity of the YIG oscillator by providing different external resilient structures supporting the enclosure. The resilient structures are arranged so as to embody a mechanical filter between the external mechanic structure and the very YIG oscillator.
Hitherto this has typically been taken care of by the purchaser of the YIG oscillator, who has had to make an application specific solution. This, more or less inevitably, has resulted in comparatively large resilient structures. Consequently it is desirable to provide a complete YIG oscillator relieving the purchaser of his problem of resiliently supporting the YIG oscillator.
Additionally, the arrangement of an external resilient structure between the enclosure of the YIG oscillator and the external mechanical structure, gives rise to another problem. The problem relates to how to resiliently transmit the microwave output signal from the YIG oscillator to an external microwave circuit, which is supported by the external mechanic structure.
Another prior art solution to the problem of mechanical vibrations is disclosed in U.S. Pat. No. 5,652,550, where the YIG oscillator is enclosed and supported by an aerogel structure. A second outer enclosure is provided in order to hold the aerogel. Also this solution leads to an undesired size of the resulting device. Additionally, like the above described known resilient structures the solution according to U.S. Pat. No. 5,652,550 suffers from the lack of a resilient arrangement for transmitting the microwave output signal from the YIG oscillator to the external circuitry.